Cell Growth and Division
Purpose of the cell cycle which
includes the mitosis:
-To produce new and identical body cells with identical
copies of DNA.
-Example: 1 skin cell will divide into 2 new and
identical skin cells
-All human body cells contain :
46 chromosomes or pieces of DNA
-23 from your mom
-23 from your dad
Mitosis produces body cells known as
2N or diploid cells.
Known as 2N or
diploid because
they contain 2 of
every chromosome
in each cell.
-one of each from
your mother
-one of each from
your dad
When a sperm with 23
chromosomes (1N)
fertilizes an
egg with 23
chromosomes (1N) it
produces the first body
cell, called the 2N
zygote
which has a total of 46
chromosomes.
Fertilization:
1N sperm unites
with1N
1N sperm
11 N egg
is
fertilized
by
a
egg creating a 2N zygote.
creating a 2N zygote or body cell.
Twin Formation
Identical twins:
-1 sperm and 1 egg unit forming one zygote.
-Zygote goes through mitosis creating two identical cells.
-The two identical cells split apart and both form into a fetus/baby.
-Babies must be of the same sex.
Fraternal twins:
-2 separate sperm fertilize 2 separate eggs forming two separate
zygotes.
-Each zygote goes through mitosis creating 2 separate babies.
-The two babies may be the same sex or of opposite sex.
DNA
-DNA is our
genetic code
-we inherit our DNA from
our parents
-DNA has the code for making
all of our proteins which determine our traits.
Examples of human traits
1. DNA is located in the
nucleus
of every cell in a relaxed,
uncondensed form known
as chromatin.
2. DNA supercoils into
chromatids the loops of
tightly coiled DNA of a
chromosome.
Chromosome:
-1 piece of DNA
Gene:
-1 segment of
DNA on a
chromosome that
codes for a
protein.
Allele:
-a specific form
of a gene
Allele:
A specific form of a gene
Each trait has 2 possible forms
Dominant form or allele:
The overpowering form of a gene
Represented by a capital letter
Recessive form or allele:
The weaker form of a gene
Represented by a lower case letter
2 alleles combine to determine a trait.
1 allele/gene from the sperm
1 allele/gene from the sperm
Phenotype:
A physical trait that you can see
Examples:
Red hair, blue eyes, etc…
Genotype:
The genetic make up /gene or allele
combination
Three types of genotypes:
BB…..
Homozygous dominant
Bb……
Heterozygous
bb…….
Homozygous recessive
Law of Dominance
Anytime a dominant allele is present
the dominant trait will be seen, it
overpowers the recessive allele.
Example:
Black fur is dominant ………… B
White fur is recessive………… b
B
b
B
B
b
b
Bb
BB
b
B
bb
Let us review:
Purpose of the cell cycle which includes the
mitosis:
To produce new and identical body cells with
identical copies of DNA.
-Example: 1 skin cell will divide into 2 new and
identical skin cells
One cell cycle is made up of:
1. Interphase
Gap 1
Synthesis phase
Gap 2
2. Mitosis
Prophase
Metaphase
Anaphase
Telophase
3. Cytokinesis
DNA Replicates
Cell divides in half
Interphase
• A. Occurs in three sub phases:
– Gap 1: Cell grows and matures from a daughter cell into
a parent cell.
– S phase: DNA is replicates
– Gap 2: New and needed organelles are formed
• B. DNA is in a loosely coiled, uncondensed
from of chromatin.
• C. Two pairs of centrioles are present outside
the nucleus.
Gap 0
Non dividing cells like nerve, brain and heart
cells do not go through cell division.
Therefore, they remain in Interphase for their
entire existence. This is referred to as Gap 0.
Interphase
Prophase
• A. First phase of
mitosis.
• B. Longest phase of
mitosis.
• C. Sets the stage for
the rest of cell
division.
Early prophase
• 1. Nucleus and nucleolus breakdown into
their components of proteins, lipids and
carbs.
• 2. Chromatin supercoils into chromatids.
• 3. Centrioles pairs split apart and move to
opposite sides of the cell/the poles.
• 4. Centrioles stretch spindle
fibers/microtubules across the cell.
Late prophase
Metaphase
• A. Second phase of mitosis
• B. Shortest phase of mitosis.
– 1. Replicated chromosomes move to the
middle/equator of the cell.
- 2. Each chromosome attaches to its own
spindle fiber using the centromere.
Metaphase
Anaphase
• A. Third phase of mitosis
• B. Replicated chromosomes split apart and
ASTERS
move away to opposite poles.
1. Sister chromatids
split apart from each
other.
2. One single,
unreplicated copy of
the chromosome is
at each pole.
3. Spindle fibers break
down.
Asters
• End of spindle fibers at the pole
• Push against cell membrane causing the cell to
elongate or get wider.
Anaphase
Telophase
• A. Final phase of mitosis
• B. Exact opposite of prophase.
– 1. A nucleus reappears around
each set of chromosomes at the
poles
- 2. A nucleolus reappears in each
nucleus.
- 3. Chromatid uncoils into
chromatin.
Telophase
Cytokinesis
• A. One cell divides into two new identical
daughter cells.
– Animal cells:
• Cell membrane pinches together forming a cleavage
furrow.
• Two ends eventually join separating the one cell into
two cells.
Plant cells:
- The formation of a cell plate occurs.
- The cell plate is a collection of sacks of cellulose that
collect in the center of the cell.
-The cell plate eventually matures into a cell wall.
Cytokinesis
End Result:
One mature parent cell divides into two new and
genetically identical daughter cells.
Cell starts over…………………………hence the cell cycle.
MITOSIS
Cell division video